EM-based Column Widths?

As Gunther Pilz first pointed out to me, EMs have a nice advantage in that they allow your columns to scale in size with the user's base font. As the user increases his/her font size, so will the columns. This can have some interesting results with low-res users viewing your page with a super large font size, but overall I think it's an interesting approach that is worth consideration. At the very least, the pros and cons that come with this approach should offset each other.